Ahh, well... it depends. Usually you see it in animated series and games because designing new models is rather costly and it helps with branding to keep outfits the same.
So I think some comics mimic this to maximize a reader's memory. When you see that character in the same outfit again you might say, "Hey, I remember this orange sweater guy." Sometimes it's essential for budding artists that suffer from same-face syndrome. I've read some comics where I literally couldn't recognize a character when they changed clothes. D:
Also it might be a storytelling thing, like you said. Maybe they just don't have any other clothes. XD In that case, they better look lived in like Masahiro's clothes in Grassblades.
One more point too, it might have to do do with how the comic is paced. One day in the comic world might take a year of posting in real time. That's what's happening to me anyway. So, the characters are going to keep the outfits they have until the day in the comic passes. ...Which won't be until Chapter 3. So that can distort things as well. XD